CN114506830B - Preparation method of phosphate coated positive electrode active material - Google Patents

Preparation method of phosphate coated positive electrode active material Download PDF

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CN114506830B
CN114506830B CN202011284593.0A CN202011284593A CN114506830B CN 114506830 B CN114506830 B CN 114506830B CN 202011284593 A CN202011284593 A CN 202011284593A CN 114506830 B CN114506830 B CN 114506830B
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positive electrode
active material
electrode active
phosphate
coating dispersion
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CN114506830A (en
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武怿达
黄学杰
詹元杰
马晓威
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Institute of Physics of CAS
Songshan Lake Materials Laboratory
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Songshan Lake Materials Laboratory
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    • C—CHEMISTRY; METALLURGY
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/37—Phosphates of heavy metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G45/00—Compounds of manganese
    • C01G45/12—Manganates manganites or permanganates
    • C01G45/1221—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof
    • C01G45/1242—Manganates or manganites with a manganese oxidation state of Mn(III), Mn(IV) or mixtures thereof of the type [Mn2O4]-, e.g. LiMn2O4, Li[MxMn2-x]O4
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a preparation method of a phosphate coated positive electrode active material, which comprises the following steps: adding a phosphorus source and ammonia water into deionized water, and mixing to form a coating dispersion liquid, wherein the phosphorus source is one or more of ferric phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, copper phosphate and magnesium phosphate; coating the coating dispersion liquid on the surface of a positive electrode active material with a spinel structure, and drying to obtain powder; sintering the dry powder at 200-600 ℃.

Description

Preparation method of phosphate coated positive electrode active material
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a preparation method of a phosphate coated positive electrode active material.
Background
Compared with other chargeable battery systems, the lithium ion secondary battery has the advantages of high working voltage, light weight, small volume, no memory effect, low self-discharge rate, long cycle life, high energy density and the like, and is widely applied to mobile terminal products such as mobile phones, notebook computers, tablet computers and the like. In recent years, electric vehicles have been rapidly developed under the promotion of governments and automobile manufacturers in various countries in view of environmental protection,and the lithium ion secondary battery becomes an ideal power source of a new generation of electric automobiles by virtue of its excellent performance. Currently, positive electrode active materials of lithium ion secondary batteries of interest can be broadly divided into three categories: with lithium cobaltate (LiCoO) 2 ) As a representative layered material, lithium iron phosphate (LiFePO 4 ) Olivine-type material and lithium manganate (LiMn 2 O 4 ) Is a typical spinel structure material. Among these materials, spinel-structured materials have been widely studied for their advantages of environmental protection of raw materials, low cost, simple process, high safety, good doubling performance, and the like.
Manganese-based high-voltage materials, which are advanced positive electrode active materials, are considered as positive electrode active materials that are most likely to be the next-generation high-performance lithium batteries. In particular, the theoretical specific capacity of the nickel lithium manganate with spinel structure is 146.7mAh/g, and the working voltage is 4.7Vvs. Li/Li + The theoretical capacity density can reach 695Wh/kg, and is an ideal material for lithium ion secondary batteries for electric vehicles in the future. The lithium-rich material with the layered structure has specific capacity of more than 350mAh/g and belongs to a future better anode material.
However, for the current manganese-based high-voltage materials, H is generated under high pressure due to the traditional carbonate electrolyte 2 O (H is inevitably contained in trace amount even in fresh electrolyte) 2 O)，H 2 O and conventional carbonate electrolyte (containing LiPF 6 ) The reaction generates HF, which further corrodes the surface of the positive electrode material, so that the surface of the positive electrode active material is dissolved, and finally, the active substances are reduced. Meanwhile, for lithium nickel manganese oxide positive electrode active materials, mn ions dissolved in the positive electrode migrate to the negative electrode and deposit on the negative electrode, so that the decomposition of a solid electrolyte interface film (SEI film) on the surface of the negative electrode is promoted, active lithium in a battery system is consumed, and capacity is reduced.
In order to solve the technical problem, it is proposed to coat and modify the positive electrode active material, wherein the coating with lithium phosphate can achieve a good effect, the lithium phosphate is high-pressure resistant, can absorb hydrofluoric acid, does not contain transition metal ions, and has no side effect on the battery. The conventional lithium phosphate coating method includes: (1) Mixing the anode material to be coated with a lithium phosphate solid phase and calcining to coat; (2) And coating the positive electrode material to be coated with lithium phosphate by using a sol-gel method. However, in the conventional lithium phosphate coating method, lithium phosphate is difficult to uniformly distribute on the surface of the positive electrode active material due to lattice mismatch, meanwhile, the coating effect of the conventional solid phase coating method is influenced by the particle size of the coating, the larger particle size of the coating is unfavorable for coating the coating, and the coating needs to be nanocrystallized to obtain smaller particles of the coating, so that the cost is high. For sol-gel coating, organic matters such as citric acid are introduced into the system in the coating process, and the organic matters are required to be sintered at a higher temperature to be removed, and most of the coating matters are agglomerated at the high temperature, so that the subsequent uniform surface coating is not facilitated.
Disclosure of Invention
Based on this, it is necessary to provide a method for preparing a phosphate-coated positive electrode active material, which can uniformly distribute lithium phosphate on the surface of the positive electrode active material.
The invention provides a preparation method of a phosphate coated positive electrode active material, which comprises the following steps:
s10, adding a phosphorus source and ammonia water into deionized water, and mixing to form a coating dispersion liquid, wherein the phosphorus source is one or more of ferric phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, copper phosphate and magnesium phosphate;
step S20, coating the coating dispersion liquid on the surface of a positive electrode active material with a spinel structure, and drying to obtain powder; and
and step S30, sintering the dry powder at 200-600 ℃.
In one embodiment, the positive electrode active material has the chemical formula LiMn 2-x A x O y Wherein x is more than or equal to 0 and less than or equal to 0.7,3.8, y is more than or equal to 4.2, and A is one or more of alkaline earth metal elements, metalloid elements or transition metal elements.
In one embodiment, a is selected from one or more of Li, mg, zn, ni, mn, fe, co, ti, Y, sc, ru, cu, mo, ge, W, zr, ca, ta, al, nb, B, si, F, S, P and Sr.
In one embodiment, the formula LiMn 2-x A x O y Wherein A is selected from Co and/or Ti;
preferably, 0.ltoreq.x.ltoreq.0.5;
the particle diameter of the positive electrode active material is preferably 0.1 μm to 30 μm, more preferably 0.2 μm to 10 μm, and still more preferably 0.2 μm to 0.5 μm.
In one embodiment, the coating dispersion further comprises a lithium precursor, wherein the lithium precursor is lithium hydroxide.
In one embodiment, the molar concentration of the ammonia water is 5mol/L to 50mol/L, and the mass ratio of the phosphorus source, the ammonia water and the lithium precursor is (1 to 5): (20-50): (0.1-2).
In one embodiment, the mass ratio of the coating dispersion liquid and the positive electrode active material is (30 to 300): (20-200).
In one embodiment, step S20 includes the steps of:
placing the positive electrode active material in a closed container with the ambient temperature of 50-200 ℃, and rolling the positive electrode active material by utilizing airflow or mechanical stirring;
spraying the coating dispersion liquid into the closed container at a spraying speed of 1 g/s-200 g/s; and
and after spraying, drying at 100-200 ℃.
In one embodiment, step S20 includes the steps of:
the positive electrode active material is immersed in the coating dispersion liquid, and is dried by a spray drying method or a vacuum rake drying method.
In one embodiment, the spray drying method comprises the steps of:
spraying the coating dispersion liquid impregnated with the positive electrode active material into a cavity with hot air circulation at a spraying speed of 5 g/min-5 kg/min, and staying in the cavity until drying, wherein the temperature of hot air is 100-200 ℃.
In one embodiment, the spray drying method comprises the steps of:
and (3) placing the coating dispersion liquid impregnated with the positive electrode active material into a closed container for heating, wherein the heating temperature is 80-200 ℃, stirring and vacuumizing are carried out while heating, so that the solvent volatilizes.
According to the preparation method of the phosphate coated positive electrode active material, the phosphate containing metal elements is used as a phosphorus source, ammonia water is used as a solvent to form coating liquid, the ammonia water can be used for complexing the phosphate to form a complex, so that the phosphate can be more uniformly formed on the surface of the positive electrode active material without agglomeration, and the technical staff first find that nickel, cobalt, manganese, copper or magnesium metal elements contained in the phosphate can be diffused into particles in the low-temperature sintering process after the complexing action of the ammonia water, so that a transition layer is formed in the spinel structured positive electrode active material. The transition layer is favorable for the coating layer to be uniformly distributed on the spinel-structure positive electrode active material, plays a role in stabilizing the coating layer and the spinel-structure positive electrode active material, and forms a stable structure between the coating layer and the spinel-structure positive electrode active material.
Drawings
Fig. 1 is a flowchart of a preparation method of a phosphate coated positive electrode active material according to the present invention.
Detailed Description
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
Except where shown or otherwise indicated in the operating examples, all numbers expressing quantities of ingredients, physical and chemical properties, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term "about". For example, therefore, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can be varied appropriately by those skilled in the art utilizing the teachings disclosed herein seeking to obtain the desired properties. The use of numerical ranges by endpoints includes all numbers subsumed within that range and any range within that range, e.g., 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, 5, and the like.
A core-shell structure is generally defined as an orderly assembled structure formed by one material encapsulating another material by chemical bonds or other forces. The core-shell like structure "core" and "shell" as defined in the present invention are virtually integral. The modified lithium nickel manganese oxide material structure of the present invention comprises two phases, resulting in a microstructure of the surface layer different from that of the interior of the material, the interior of the material so formed is referred to as the "core", the surface layer is referred to as the "shell", and the material of such structure is defined as a core-shell like structure.
Referring to fig. 1, an embodiment of the invention provides a preparation method of a phosphate coated positive electrode active material, which includes the following steps:
s10, adding a phosphorus source and ammonia water into deionized water, and mixing to form a coating dispersion liquid, wherein the phosphorus source is one or more of ferric phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, copper phosphate and magnesium phosphate;
s20, coating the coating dispersion liquid on the surface of a positive electrode active material with a spinel structure, and drying to obtain powder; and
s30, sintering the dry powder at 200-600 ℃.
According to the preparation method of the phosphate coated positive electrode active material, the phosphate containing metal elements is used as a phosphorus source, ammonia water is used as a solvent to form coating liquid, the ammonia water can be used for complexing the phosphate to form a complex, so that the phosphate can be more uniformly formed on the surface of the positive electrode active material without agglomeration, and the technical staff first find that nickel, cobalt, manganese, copper or magnesium metal elements contained in the phosphate can be diffused into particles in the low-temperature sintering process after the complexing action of the ammonia water, so that a transition layer is formed in the spinel structured positive electrode active material. The transition layer is favorable for the coating layer to be uniformly distributed on the spinel-structure positive electrode active material, plays a role in stabilizing the coating layer and the spinel-structure positive electrode active material, and forms a stable structure between the coating layer and the spinel-structure positive electrode active material.
Preferably, the phosphorus source is cobalt phosphate and/or manganese phosphate.
The chemical formula of the positive electrode active material LiMn 2-x A x O y Wherein x is more than or equal to 0 and less than or equal to 0.7,3.8, y is more than or equal to 4.2, the A element is a doping element, and the doping element is used for replacing the transition metal element Mn. In some embodiments, doping element a may be represented by the formula Σwiai, wi being the atomic percent of Ai in the entire doping element a, Σwi=1, where 1+.i+.16, preferably 1+.i+.5, more preferably 1+.i+.3.
In one embodiment, a is selected from one or more of Li, mg, zn, ni, mn, fe, co, ti, Y, sc, ru, cu, mo, ge, W, zr, ca, ta, al, nb, B, si, F, S, P and Sr. Preferably, a is selected from Co and/or Ti.
Further preferred, the formula LiMn 2-x A x O y In 0.ltoreq.x.ltoreq.0.5, in some embodiments x is 0, in some embodiments 0.1.ltoreq.x.ltoreq.0.5.
In a preferred embodiment, the positive electrode active material has the formula LiMn 2 O 4 Or LiNi 0.5 Mn 1.5 O 4 。
The particle diameter of the positive electrode active material may be any value between 0.1 μm and 30 μm, and may be, for example, 0.2 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, preferably 0.2 μm to 10 μm, and more preferably 0.2 μm to 0.5 μm.
In some embodiments, the coating dispersion also contains a lithium precursor. The lithium precursor can supplement lithium to the interface of the active material and provide a source of lithium for the subsequent generation of lithium phosphate or lithium phosphate salt, preferably the lithium precursor is lithium hydroxide.
In the phosphate coating layer formed by the preparation method of the phosphate coated positive electrode active material, the phosphate is lithium phosphate or lithium phosphate salt containing nickel, cobalt, manganese, copper or magnesium metal elements. For example LiCoPO 4 、LiNiPO 4 、LiMnPO 4 、LiCuPO 4 、LiMgPO 4 And Li (lithium) 3 PO 4 One or more of the following.
The molar concentration of the ammonia water is 5mol/L to 50mol/L. Ammonia water is used as a solvent, and is volatile, so that other impurities can be effectively prevented from being introduced in the sintering process.
The mole ratio of the phosphorus source, the ammonia water and the lithium precursor can be (1-5): (20-50): (0.1-2).
The mass ratio of the coating dispersion liquid and the positive electrode active material may be (30 to 300): (20-200).
In step S20, the coating dispersion is formed on the surface of the positive electrode active material having a spinel structure, and the powder may be obtained by various methods.
In an embodiment, the preparation method of the dry powder may include the following steps:
s21, placing the positive electrode active material in a closed container with the environmental temperature of 50-200 ℃, and rolling the positive electrode active material by utilizing airflow or mechanical stirring;
s23, spraying the coating dispersion liquid into the closed container at a spraying speed of 1 g/S-200 g/S; and
s25, drying at 100-200 ℃ after spraying.
In the liquid phase synthesis method, as solid-liquid contact is performed, continuous interface reaction exists between phases, and in order to avoid the influence caused by the interface reaction, better modification can be realized by effectively controlling the interface reaction, so that the anode active material with better electrochemical performance is prepared. Preferably, by adopting a method of spraying the coating dispersion liquid onto the surface of the positive electrode active material, the solid-liquid interface reaction time can be controlled, and the thickness of the coating dispersion liquid formed on the positive electrode active material can be precisely controlled, so that the coating dispersion liquid has better modification effect, and the prepared phosphate coated positive electrode active material has better electrochemical performance.
Preferably, in step S23, the solid content of the coating dispersion is 20% to 40%, and the spraying speed is 1g/S to 10g/S. The thickness of the coating dispersion formed on the positive electrode active material can be adjusted by adjusting the solid content of the coating dispersion and the ejection speed of the coating dispersion, and in this range, the solid content of the coating dispersion and the ejection speed of the coating dispersion can make the electrochemical performance of the positive electrode active material better.
The ambient temperature of the closed container is preferably 80-120 ℃.
In another embodiment, the method for preparing the dry powder may include the steps of:
and S22, immersing the positive electrode active material in the coating dispersion liquid, and drying by adopting a spray drying method or a vacuum rake drying method.
Further, when the dry powder is prepared in step S22, the coating dispersion preferably further includes a stabilizer that is easily vaporized. In step S22, the solid phase and the liquid phase in the coating dispersion liquid are easy to be layered or settled in the drying process, and the addition of the stabilizer can effectively avoid the separation of the solid phase and the liquid phase, thereby being beneficial to the uniform distribution of the coating dispersion liquid on the surface of the positive electrode active material and enabling the doping interface of the finally prepared positive electrode active material to be more uniform.
The stabilizer may include one or more of polyvinyl alcohol, polyethylene glycol, acrylonitrile multipolymer, polybutyl acrylate, and polyacrylonitrile.
In one embodiment, step S22 is performed by spray drying, including the following steps:
s24, spraying the coating dispersion liquid impregnated with the positive electrode active material into a cavity with hot air circulation at a spraying speed of 5 g/min-5 kg/min, and staying in the cavity until drying, wherein the temperature of hot air is 100-200 ℃.
The above spray drying method can spray the coating dispersion impregnated with the positive electrode active material into very fine mist droplets, which can be rapidly vaporized in a heated air circulation to form a dry powder. Therefore, the method has higher efficiency for preparing the dry powder.
In yet another embodiment, step S22 of drying by vacuum rake drying includes the steps of:
and S28, placing the coating dispersion liquid impregnated with the positive electrode active material into a closed container for heating, wherein the heating temperature is 80-200 ℃, stirring and vacuumizing are carried out while heating, and the solvent is volatilized.
The vacuum rake drying method can control the interface condition of the modified material by controlling the heating temperature and the stirring speed, and adjust the interface reaction between the phosphorus source and the positive electrode active material to be modified, so that the finally formed phosphate coating is more uniform.
The heating temperature of the vacuum rake drying method may be 80 to 200 ℃, preferably 100 to 150 ℃. The stirring speed may be 20 to 400 rpm, preferably 50 to 100 rpm.
In step S30, the sintering may be performed under oxygen, air, nitrogen, an atmosphere containing a reducing gas (e.g., hydrogen), or an inert atmosphere (e.g., argon). Preferably, the specific operation of the sintering process is as follows: heating to 200-600 ℃ at a heating rate of 0.5-10 ℃/min, sintering for 0.5-10 h, and cooling to room temperature at a cooling rate of 0.5-10 ℃/min.
The invention further provides a phosphate coated positive electrode active material obtained by the preparation method of the phosphate coated positive electrode active material.
The phosphate coated positive electrode active material includes lithium-containing compound particles having a spinel structure and a phosphate coating layer coated on the surface thereof. The lithium-containing compound particles have a transition layer containing a diffusing element that enters the lithium-containing compound particles by sintering.
In one embodiment, the lithium-containing compound particles have the formula LiMn 2-x A x O y In the chemical formula, x, y and A are as described above.
In an embodiment, the diffusing element is one or more of Ni, co, mn, cu and Mg.
The phosphate in the phosphate coating layer can be LiCoPO 4 、LiNiPO 4 、LiMnPO 4 、LiCuPO 4 、LiMgPO 4 And Li (lithium) 3 PO 4 One or more of the following.
In some embodiments, the phosphate is Li 3 PO 4 The diffusing element is one or more of Ni, co, mn, cu. In other embodiments, the phosphate is LiMgPO 4 The diffusion element is Mg.
The thickness of the phosphate coating may be any value between 1nm and 50nm, and for example, 2nm, 5nm, 8nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, preferably 5nm to 15nm are also included.
The coverage of the phosphate coating on the surface of the lithium-containing compound particles may be anywhere between 1% and 100%. In some embodiments, the phosphate coating has a coverage of the surface of the lithium-containing compound particles from 10%, 20%, 30%, 40%, 50%, or 60% at the lower endpoint to 50%, 60%, 70%, 80%, or 90% at the upper endpoint. For example, in some preferred embodiments, the phosphate coating has a coverage of 20% to 90%, and in some more preferred embodiments 60% to 80%, on the surface of the lithium-containing compound particles.
In some embodiments, the phosphate coating may be composed of a single layer of phosphate particles. In some embodiments, the phosphate particles have a particle size of 1nm to 50nm, and in some preferred embodiments the phosphate particles have a particle size of 5nm to 20nm.
The thickness of the transition layer may be any value between 0.1 μm and 15 μm, for example, also including 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm.
In some preferred embodiments, the thickness of the transition layer is 100nm to 250nm.
The transition layer may be distributed between 0nm and 10nm, preferably between 0nm and 5nm, from the surface of the lithium containing compound particles.
The phosphate coated positive electrode active material provided according to the present invention, wherein the phosphate coating layer and the transition layer may be measured by any method known in the art. For example, the type of phosphate coating can be determined by X-ray diffraction and X-ray photoelectron spectroscopy, and the distribution and content of each element in the transition layer can be measured using an X-ray spectral line scan of a spherical aberration correcting transmission electron microscope.
The invention further provides a positive electrode of the lithium ion secondary battery, which comprises a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector, wherein the positive electrode active material layer comprises the phosphate coated positive electrode active material.
As the positive electrode current collector, a conductive element formed of a highly conductive metal as used in the positive electrode of the lithium ion secondary battery of the related art is preferable. For example, aluminum or an alloy including aluminum as a main component may be used. The shape of the positive electrode current collector is not particularly limited, as it may vary depending on the shape of the lithium ion secondary battery, etc. For example, the positive electrode current collector may have various shapes such as a rod shape, a plate shape, a sheet shape, and a foil shape.
The positive electrode active material layer further includes a conductive additive and a binder.
The conductive additive may be a conductive additive conventional in the art, and the present invention is not particularly limited thereto. For example, in some embodiments, the conductive additive is carbon black (e.g., acetylene black or Ketjen black).
The binder may be a binder conventional in the art, and the present invention is not particularly limited, and may be composed of polyvinylidene fluoride (PVDF), and may also be composed of carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR). In some embodiments, the binder is polyvinylidene fluoride (PVDF).
Still further, the present invention provides a lithium ion secondary battery comprising:
a positive electrode as described above;
a negative electrode including a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector;
separator and electrolyte.
As a current collector of the negative electrode,
the negative electrode, separator and electrolyte may employ a negative electrode current collector, separator and electrolyte material conventional in the art, and the present invention is not particularly limited thereto.
The negative electrode current collector may be copper, and the shape of the negative electrode current collector is also not particularly limited, and may be in the shape of a rod, a plate, a sheet, and a foil, which may vary depending on the shape of the lithium ion secondary battery, etc. The anode active material layer includes an anode active material, a conductive additive, and a binder. The anode active material, the conductive additive, and the binder are also conventional materials in the art. In some embodiments, the negative electrode active material is lithium metal. The conductive additive and the binder are described above and are not described in detail herein.
The separator may be a separator used in a usual lithium ion secondary battery, and examples thereof include microporous films made of polyethylene or polypropylene; porous polyethylene films and polypropylene multilayer films; a nonwoven fabric formed of polyester fibers, aramid fibers, glass fibers, and the like; and a base film formed by attaching ceramic fine particles such as silica, alumina, titania, etc. to the surface of the base film. In some embodiments, the separator is a three-layer film of PP/PE/PP coated on both sides with aluminum oxide.
The electrolyte may include an electrolyte and a non-aqueous organic solvent. The electrolyte is preferably LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 . The nonaqueous organic solvent may be a carbonate, an ester, or an ether. Among them, carbonates such as carbonic acid can be preferably usedEthylene (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC). In some embodiments, the electrolyte is LiPF 6 The concentration of (C) ethylene carbonate/dimethyl carbonate (DMC) nonaqueous electrolyte is 1mol/L, wherein the volume ratio of the EC to the DMC is 1:1.
The following examples are intended to illustrate the present invention in further detail to aid those skilled in the art and researchers in further understanding the present invention, and the technical conditions and the like are not to be construed as limiting the present invention in any way. Any modification made within the scope of the claims of the present invention is within the scope of the claims of the present invention.
Example 1
(1) A coating dispersion was formed by uniformly mixing 0.3g of nickel phosphate, 0.15g of lithium hydroxide and 25mL of aqueous ammonia (molar concentration: 2 mol/L).
(2) 10g LiMn 2 O 4 (particle diameter of 200 nm) is placed in a reaction chamber with an ambient temperature of 100 ℃, and the positive electrode active material LiMn is caused to flow by an air flow 2 O 4 And (5) rolling.
(3) Spraying the coating dispersion liquid in the step (1) into a reaction chamber from a nozzle with the diameter of 1 mu m to 1mm, so that the coating dispersion liquid is formed on the surface of the positive electrode active material.
(4) And after the coating liquid is sprayed, directly drying at 120 ℃ to obtain dry powder.
(5) And (3) sintering the dried powder in the step (4) in air at 450 ℃ for 3 hours to obtain the phosphate coated positive electrode active material.
Example 2
(1) A coating dispersion was formed by uniformly mixing 0.3g of nickel phosphate, 0.1g of lithium hydroxide and 25mL of aqueous ammonia (molar concentration: 2 mol/L).
(2) 10g LiMn 2 O 4 (particle diameter of 200 nm) was immersed in the coating dispersion in step (1), and then the immersion solution was sprayed from a nozzle having a diameter of 1 μm to 1mm into a cavity having a circulation of hot air at a temperature of 100 ℃.
(3) And after the coating liquid is sprayed, drying at 100 ℃ to obtain dry powder.
(4) And (3) sintering the dried powder in the step (3) in air at 450 ℃ for 3 hours to obtain the phosphate coated positive electrode active material.
Example 3
(1) A coating dispersion was formed by uniformly mixing 0.3g of nickel phosphate, 0.1g of lithium hydroxide and 25mL of aqueous ammonia (molar concentration: 2 mol/L).
(2) 10g LiMn 2 O 4 Immersing the coated dispersion in the step (1) (with the particle size of 200 nm), then placing the immersed solution into a closed cavity for heating, stirring and vacuumizing while heating, wherein the heating temperature is 120 ℃, the stirring speed is 60 revolutions per minute, and volatilizing the solvent to obtain dry powder.
(3) And (3) sintering the dried powder in the step (2) in air at 450 ℃ for 3 hours to obtain the phosphate coated positive electrode active material.
Example 4
Substantially the same as in example 1, except that LiMn was used 2 O 4 Replaced by LiNi 0.5 Mn 1.5 O 4 。
Example 5
The preparation method was substantially the same as in example 1, except that the nickel phosphate was replaced with cobalt phosphate.
Example 6
The preparation method was substantially the same as in example 1, except that nickel phosphate was replaced with manganese phosphate.
Example 7
The preparation method was substantially the same as in example 1, except that the nickel phosphate was replaced with copper phosphate.
Example 8
The preparation method was substantially the same as in example 1, except that nickel phosphate was replaced with magnesium phosphate.
Comparative example 1
The preparation method was substantially the same as that of example 1, except that ammonia was not added.
Performance testing
The phosphate-coated positive electrode active materials prepared in examples 1 to 8 were assembled into button cells according to the following procedure.
(1) Preparation of a positive electrode sheet the positive electrode active material prepared in the example, carbon black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder were dispersed in N-methyl-pyrrolidone (NMP) in a weight ratio of 80:10:10, and uniformly mixed to prepare a uniform positive electrode slurry. Uniformly coating the uniform positive electrode slurry on an aluminum foil current collector with the thickness of 15 mu m, drying at 55 ℃ to form a pole piece with the thickness of 100 mu m, and placing the pole piece under a roller press for rolling (the pressure is about 1MPa x 1.5 cm) 2 ) Cutting into wafers with the diameter of phi 14mm, then placing the wafers in a vacuum oven for drying at 120 ℃ for 6 hours, naturally cooling, and taking out the wafers to be placed in a glove box for serving as the positive electrode plate.
(2) Assembled lithium ion secondary battery
In a glove box filled with inert atmosphere, taking a metal carp as a negative electrode of a battery, placing a PP/PE/PP diaphragm coated with aluminum oxide on both sides between the positive electrode and the negative electrode, dropwise adding 1M of common carbonate electrolyte, taking the positive electrode plate prepared in the step (1) as the positive electrode, and assembling the button battery with the model CR 2032.
High temperature cycle test:
and standing the prepared button cell for 10 hours at room temperature (25 ℃), then performing charge-discharge activation on the button cell, and then performing charge-discharge cycle test on the prepared button cell by adopting a blue cell charge-discharge tester. First, the cycle was continued at 0.1C for 1 week and then at 0.2C for 4 weeks at room temperature (25 ℃) with the charge-discharge voltage of the battery controlled to be in the range of 3V to 4.3V. Then, the button cell was transferred to a high temperature environment of 55 ℃ and the cycle was continued for 50 weeks at a rate of 0.2C while controlling the charge-discharge voltage range of the battery to be still 3V to 4.3V.
In the performance test of the button cell prepared from the positive electrode active material of example 2, the charge-discharge voltage of the cell was controlled to be 3.5V to 4.9V.
And the anode active material LiMn before coating 2 O 4 、LiNi 0.5 Mn 1.5 O 4 As a control, the measured dataListed in table 1.
TABLE 1 electrochemical Properties of Positive electrode active materials of various examples of the invention
Figure BDA0002781920120000131
As can be seen from the data of the above table, compared with the original positive electrode active material LiMn 2 O 4 、LiNi 0.5 Mn 1.5 O 4 And comparative example 1, the positive electrode active materials prepared in examples 1 to 8 of the present invention were better in electrochemical properties.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (10)

1. The preparation method of the phosphate coated positive electrode active material is characterized by comprising the following steps of:
s10, adding a phosphorus source and ammonia water into deionized water, and mixing to form a coating dispersion liquid, wherein the phosphorus source is one or more of ferric phosphate, nickel phosphate, cobalt phosphate, manganese phosphate, copper phosphate and magnesium phosphate;
step S20, coating the coating dispersion liquid on the surface of a positive electrode active material with a spinel structure, and drying to obtain powder, wherein the chemical formula of the positive electrode active material is LiMn 2-x A x O y Wherein x is more than or equal to 0 and less than or equal to 0.7,3.8 and y is more than or equal to 42, A is selected from one or more of alkaline earth metal elements, metalloid elements or transition metal elements; and
and step S30, sintering the dry powder at 200-600 ℃.
2. The method for producing a phosphate coated positive electrode active material according to claim 1, wherein a is one or more selected from Li, mg, zn, ni, mn, fe, co, ti, Y, sc, ru, cu, mo, ge, W, zr, ca, ta, al, nb, B, si, F, S, P and Sr.
3. The method for producing a phosphate-coated positive electrode active material according to claim 1, wherein the particle diameter of the positive electrode active material is 0.1 μm to 30 μm.
4. The method for producing a phosphate coated positive electrode active material according to claim 1, wherein the coating dispersion further contains a lithium precursor, and the lithium precursor is lithium hydroxide.
5. The method for preparing a phosphate coated positive electrode active material according to claim 1, wherein the molar concentration of the ammonia water is 5mol/L to 50mol/L, and the mass of the phosphorus source, the ammonia water and the lithium precursor is (1 to 5): (20-50): (0.1-2).
6. The method for producing a phosphate-coated positive electrode active material according to claim 1, wherein the mass ratio of the coating dispersion liquid to the positive electrode active material is (30 to 300): (20-200).
7. The method for preparing a phosphate coated positive electrode active material according to claim 1, wherein step S20 comprises the steps of:
placing the positive electrode active material in a closed container with the ambient temperature of 50-200 ℃, and rolling the positive electrode active material by utilizing airflow or mechanical stirring;
spraying the coating dispersion liquid into the closed container at a spraying speed of 1 g/s-200 g/s; and
and after spraying, drying at 100-200 ℃.
8. The method for preparing a phosphate coated positive electrode active material according to claim 1, wherein step S20 comprises the steps of:
the positive electrode active material is immersed in the coating dispersion liquid, and is dried by a spray drying method or a vacuum rake drying method.
9. The method for preparing a phosphate coated positive electrode active material according to claim 8, wherein the spray-drying method comprises the steps of:
spraying the coating dispersion liquid impregnated with the positive electrode active material into a cavity with hot air circulation at a spraying speed of 5 g/min-5 kg/min, and staying in the cavity until drying, wherein the temperature of hot air is 100-200 ℃.
10. The method for preparing a phosphate coated positive electrode active material according to claim 8, wherein the method for vacuum rake drying comprises the steps of:
and (3) placing the coating dispersion liquid impregnated with the positive electrode active material into a closed container for heating, wherein the heating temperature is 80-200 ℃, stirring and vacuumizing are carried out while heating, so that the solvent volatilizes.
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CN109962227A (en) * 2019-03-29 2019-07-02 宁波容百新能源科技股份有限公司 A kind of nickelic positive electrode and preparation method thereof with uniform clad
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